This application claims the priority benefit of Taiwan application serial no. 89115462, filed Aug. 1, 2000.
1. Field of the Invention
The invention relates in general to a method of increasing the recording density and capacity of a compact disc. More particularly, this invention relates to a method that increases the recording density and capacity of a compact disc by reducing the dimensions of the mark size on the data recording region from an incident laser light beam.
2. Description of the Related Art
As multimedia technology becomes more common and popular in application, data contains increasingly larger amounts of text, sound and image information. Therefore, development in this area has focused on the enhancement of recording density and access speed. Since a compact disc has the advantages of high recording density, compact volume, long storage term, low cost, high compatibility and low failure rate, it has been the major recording medium for portable optical data storage.
FIG. 1 shows a cross sectional view of a conventional rewritable compact disc 10. The compact disc 10 comprises a transparent substrate 12, and a lower dielectric layer 14, a recording layer 16, an upper dielectric layer 18, a reflecting layer 20, and a protection layer 22 formed sequentially on the transparent substrate 12. The recording layer is made of an alloy material including tellurium (Te), germanium (Ge), and antimony (stibium, Sb) or an alloy material including indium (In), silver (Ag), tellurium (Te), germanium and antimony. The upper and lower dielectric layers 18 and 14 are used to control the thermal conductivity of the recording layer 16. The upper and lower dielectric layers 18 and 14 thus include materials such as silicon nitride, silicon oxide, zinc sulfide-silicon dioxide, titanium oxide or carbide. The compact disc is shone with a laser light beam 26 from a light source 24. The laser light beam 26 transmits through the transparent substrate 12 to reach the recording layer 18, so as to recording data into or reading data from the recording layer 18.
The recording density is determined by the dimension of the mark size on the compact disc. Specifically, the laser light beam, emitted from the light source to form the minimum mark size on the compact disc, is restricted to the diffraction limit of the laser light beam. In addition, the relationship between the diffraction limit, the wavelength (xe2x96xa1) of the laser light beam, and the numeric aperture (NA) of the objective lens is 0.6 xcex/NA. Thus, the current method to improve recording density of the compact disc is to reduce the wavelength of the laser light beam and to increase the numeric aperture of the objective lens. However, the current laser technique does not provide a narrower wavelength. Additionally, the fabrication cost for an objective lens with a larger numeric aperture is so great that fabricating such an objective lens is cost-prohibitive.
The invention provides a method of increasing the recording density and capacity of a compact disc. A compact disc is provided. The compact disc comprises a transparent substrate and a recording region on the transparent substrate. A laser light beam emitted from a light source incident on the compact disc is transmitted through the transparent substrate to reach the recording layer. The data access is then performed. Between the light source and the compact disc, an optical plate comprising a super-resolution near-field structure is inserted. The super-resolution near-field structure comprises a first dielectric layer, a second dielectric layer and an active layer sandwiched between the first and the second dielectric layers. The active layer is made of a material including gallium, germanium, arsenic, selenium, indium, tin, antimony, tellurium, and silver, or a material including gallium oxide, germanium oxide, arsenic oxide, selenium oxide, indium oxide, tin oxide, antimony oxide, tellurium oxide, and silver oxide. Transmitting through such super-resolution near-field structure, the light intensity of the laser light beam is increased and the aperture of the laser light beam is reduced.
The invention provides a super-resolution near-field structure between the light source and the compact disc to reduce the aperture of the laser light beam, so as to increase the recording density and capacity. When the laser light beam is emitted from the light source to record or read data, as the super-resolution near-field structure can increase the light intensity and reduce the aperture of the laser light. The diffraction limit of the laser light beam is thus overcome, and the recording dimension of the data recording region is reduced to increase the recording density and capacity.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.